In the paper are presented the results of exhaust gas scavenging testing for the start-up speed. The speed of SB-3.1 engine was determined by means of external driving device composed of a three-phase motor, gearbox, unidirectional clutch and control desk. The obtained findings allowed evaluation of the character of changes in the course of exhaust gas scavenging curve from a basically zero speed to the rotational speed of engine crankshaft at which the start-up takes place. Exhaust gas scavenging measurements were made in different measuring series in order to determine the effect of oil film development on cylinder bearing surface on the phenomenon of exhaust gas scavenging into crankshaft casing

This paper discusses the results of tests on the effect of compression ratio changes on engine start-up properties, the mean pressure of the compression stroke end and on the temperature of the compressed charge for the tested one cylinder SB-3.1 engine. The measurements were carried out at the ambient temperature 285 K.

In the abstract the results of studies are presented for limit values of intensity of gas blows-by through the crankcase of a piston combustion engine with spontaneous ignition in the starting phase. Attention is drawn to the fact that determining the blow magnitude during start-up is of a particular value concerning the state of the piston – ring – cylin-der system.